I received an email from David Hughes of Adelaide, Australia concerning his modifications to his Advent Heritage speakers and he’s graciously allowed me to post his story and construction details below:
David's Tri-Amped, Three way ported Advent Heritage
A Little History
I bought my Advents new in Perth (Western Australia) around 1987 I think. A few years later I moved to Queensland and shortly after that I took them to Papua New Guinea with me. Two years ago I moved to Adelaide in South Australia. If speakers could earn Frequent Flier points I could get upgraded to business class every time I fly.
My drivers suffered the same fate as yours. One day I noticed some quite bad distortion in the bottom end and when I took the grills off I noticed the foam surrounds were falling apart. At that point I noticed the small pieces of foam on the carpet. I am not sure how long a foam surround should last but I think if you live in the tropics you can divide the most optimistic life expectancy in half. On my next trip to Australia I bought four 8” poly cone drivers. I think they were a badged Dayton driver. I put them in and they sounded much better than I expected. Next to go, a couple of years later, was a tweeter. Then I bought a pair of Vifa D25 units and juxtaposed them in place of the originals. Again, the results were passable but I started using them less and less. Finally I built a pair of ESL III from E&R Audio in Perth and switched off the Advents until just about two months ago.
Flashback
About 5 years ago I decided to get a bit more serious about speaker design and bought a few software and hardware tools in an attempt to improve my success rate. I also started experimenting with open baffle systems and collecting all kinds of drivers for future projects. One of those drivers is the TangBand W8 1772. It is a full range driver which gives the best Scandinavian units a run for their money. I decided to put them in the Advent boxes. Once the original drivers have rotted out of your Advents the only good thing you can say about them is that they look nice in a sitting room. It was for this reason that I decided to rebuild them. It is of course much easier to build a completely new box.
I also decided to build them with as much flexibility as possible. The TangBand 1772 has reasonably good bass for a full range driver if put in a vented box, but I wanted to put it in sealed acoustic suspension type box. For that reason I decided to add a woofer (not a subwoofer), a Seas P21RF/P H511-08. I also decided to add a tweeter so that I wouldn’t have a gaping hole or blanking plate in upper tower. The tweeter is a North Creek D28-06S, it’s a 28mm silk dome. Probably the best tweeter made in the US in my opinion, but no longer available. I had new aluminium face-plates made by a local laser cutting company to mount the tweeters into the rectangular opening in the Advent boxes.
The end result is a system that can be configured in four different ways:
- A single full range driver
- Full range with tweeter to extend the top end
- Full range with vented woofer to extend the bottom end
- A three way system
Two volumes, ported lower chamber
To get the two 8” drivers into two different types of cabinet (vented and sealed) I had to divide the space in two, and the only place to do this is right between the drivers. This left two unequal volumes. The upper section was around 22 Litres and the lower volume was 29 Litres. So the upper one was too big and the lower one too small. Too big is easily solved by creating an internal volume for the tweeter. I designed the tweeter space to leave a volume of about 16.5 Litres which is exactly what I wanted. The bottom driver needed about 35 Litres so I extended the internal walls to meet the volume requirements.
Reduction in upper volume with separate tweeter chamber
The original cabinets are mostly made of 16mm particle board (chip board) which was inadequate when they were originally built and after 20 years of use they were starting to show the typical problem of breaking down in its inner core due to constant micro vibrations caused when playing music. Lets face it, they were built to a price. Had they had internal bracing they might last forever. I decided to line mine with 12mm MDF. This has two major advantages. Firstly you are reinforcing the walls which are now 28mm thick, and secondly, by using two materials of differing density you are actually creating a better damped material than building a new cabinet from MDF alone. That’s the theory anyway. The pictures should fill in any gaps above.
Lower volume with bracing
I won’t be putting spikes on mine. It all depends on your type of floor. In my opinion spikes are only useful if you have wall to wall carpet on a traditional timber floor. If you have tiles, spikes will mark them and you are likely to end up with a cabinet that vibrates slightly on the hard surface. You would be better off to glue a speaker to tiles.:) Spikes on bare boards do exactly the same and scratch the timber, and spikes in little cups which stop the scratching defeat the whole purpose of using spikes in the first place. You will probably have orders of magnitude more bass colouration from the room dimensions.
My crossover is a DEQX PDC 2.6HD. Invented in Australia. It’s a DSP based crossover with quite comprehensive capabilities. Best you go to www.deqx.com to read all about it. I feed it into three NAD 272 power amps. I will probably sell these soon because I have discovered over the years that they are not well suited to low impedance loads and some of my speakers drop below 2ohms at some frequencies. This causes the NAD protection circuitry to switch off the amp. Very annoying to say the least. I will be going to Chip Amps myself in due course. When paralleled they can easily handle loads down to almost 1ohm, and most of my systems are sufficiently efficient to be driven well by 20watts. I am thinking about Audio Sector’s LM4780 kit. I will probably build a 6 channel amp. However I also have the boards from a couple of QUAD 405c II amps which I will use to drive the subs I am building. They are 12” Peerless XLS drivers in acoustic suspension cabinets using a Linkwitz transform configured in the DEQX crossover.
DEQX PDC-2.6 HD Preamp Processor
How do they sound?
According to me, they are fantastic :). Actually I have only tried them in Bi amp configuration so far because I haven’t made enough speaker cables yet. Any opinion I have is of course coloured by my own genius. But I think they are quite nice. As a full range driver they are truly excellent for acoustic music like James Taylor, orchestral, and unplugged. With the bass extension they sound great on Yes, The Who and Zeppelin. I should add, don’t bother with good speakers if you listen to over mixed studio bands like The Police, Steely Dan, or The Grateful Dead. Their live albums might sound a bit better. Using the full range and tweeter together is a very nice configuration. I have them crossed over at 8KHz using the tweeter to smooth out the full range driver’s top end.
Right now the drivers are all out while I attend to the cosmetic finish. I decided not to sand back all the little dints, preferring the old patina to an as-new appearance. I gave them a coat of Australian made Scandinavian furniture oil last night and will give them another coat in a day or two.
Cabinets minus drivers
That’s it. Other speakers around here include QUAD ESL 57s, Azurahorn front loaded 160Hz horns azurahorn.com, my own subs which are almost finished, and a couple of open baffle systems of my own design. The only other unusual thing I have in mind is a re-creation of the AR MST. I have bought all the tweeters and a pair of Seas woofers for the project, just need to finish a few other projects first. I almost bought a pair in the early seventies but bought B&W DM2As instead.
Azurahorn & XLS
Finally
With hindsight, it would have been much easier to build new cabinets. Maybe just cut the front baffle off the Advents and glue it to the front of a new box for a 40mm thick front baffle, can’t do any harm.
All the best.
David Hughes
P.S. For a DSP cross-over, look at minidsp.com, I may get one of these in the future.
Bicycles